Places to find Citizen Science projects (they aren't all astronomy related):

Citizen Science Central (Cornell Lab of Ornithology) http://www.birds.cornell.edu/citscitoolkit/projects  read more »

NASA and Microsoft collaborated to create a Web site where Internet users can have fun while advancing their knowledge of Mars.  read more »

Two sites that provide web-based videos each month about what is up in the sky.

List of activities.
#10 is really good for size and scale images of planets.

Paper Plate Education: "Serving the Universe on a Paper Plate"  read more »

GalaxyZoo is the project which harnesses the power of the internet - and your brain - to classify a million galaxies.  read more »

On January 15, 2006, the Stardust spacecraft's sample return capsule parachuted gently onto the Utah desert.  read more »

In its first month of operation, the Seeing in the Dark Internet Telescope (SIDIT) has shot images of distant galaxies and nebulae in response to requests from more than 1,000 students around the worl  read more »

http://mo-www.harvard.edu/MicroObservatory/

MicroObservatory is a network of five automated telescopes that can be controlled over the Internet.  read more »